The present invention is generally directed to a method and circuits for driving a liquid crystal display device and in particular to a multiplex driving method and circuits for a multielement liquid crystal display device using a ferroelectric liquid crystal.
It is well known that if the amplitude of an electric field pulse applied to a ferroelectric liquid crystal ("FLC") molecule is large enough, the molecule can respond to a pulse having a pulse width of several microseconds and that the FLC will exhibit a memory effect, maintaining the response for a long period of time under suitable cell conditions. Thus, it was expected that a large size, high density display, with a large number of picture elements or an electronic shutter or similar device could utilize FLC. However, the relationship between the applied electric field pulse and the optical response of an FLC was not clear. This produced great uncertainty as to what waveform should be applied to an FLC in order to achieve multiplex driving.
Japanese Laid Open Publication No. 58-179890 describes a static drive method for a ferroelectric liquid crystal device. This method is not suitable for multiplex driving as it is not possible to make the DC component of the voltage applied to the (FLC) equal to zero since the FLC responds to the polarity of the applied electric field.
Additional reasons for why the static driving method is not suitable for a large picture element display is the complexity of: 1. the electrodes on a liquid crystal cell; 2. the connection of the electrodes and the ouput portions of a driver circuit; and 3. the complexity of the driver circuit itself. Thus, in order to produce large size displays, with a high density of elements, using an FLC and so as to have fast response time and memory effects, it is desirable to use a multiplex driving method suitable for an FLC.
The optical response of an FLC is not determined soley by the amplitude of the electric field pulse applied thereto. It is the area of the pulse applied to the FLC which determines the response. Thus, the light transmission state changes even for small amplitudes of the applied electric field if the pulse width is very long. This creates the difficulty of a change in the light transmission state when an electric field pulse having a polarity opposite to that of the electric field pulse which determines the light transmission state in a selecting term (and having a small amplitude and a long pulse width) is applied in a non-selecting term. As a result it is not possible to employ a multiplex driving method in the same manner as in a conventional twisted nematic liquid crystal.
Accordingly, there is a need for a method for multiplex driving of a liquid crystal device using FLC in which the application of a pulse during a non-selecting term or period does not affect the optical response of the FLC. Further, there is a need for circuitry for producing drive waveforms suitable for multiplex driving of a multielement liquid crystal display using an FLC.